1. Field of the Invention
The present invention relates to a semiconductor device with a SOI structure and a method of manufacturing the same.
2. Description of the Related Art
The substrate structure of a chip of a semiconductor device of the present invention is not limited in particular. However, the present invention is applied to a so-called SOI (Silicon On Insulator) which is the most popular structure. The SOI structure is formed by use of the techniques such as a SIMOX (Separation by Implanted Oxygen) method using ion implantation of oxygen ions, and a method of bonding silicon substrates. For example, as a chip 110 shown in FIG. 1A, the structure is formed in which an insulating film 303 and a single crystal semiconductor layer 302 are formed in this order on a support substrate 301 usually made of a silicon substrate.
The semiconductor device using the substrate having the SOI structure (hereinafter, referred to as an SOI semiconductor device) is preferable for the application requiring a high breakdown voltage. In the SOI semiconductor device, a chip is typically mounted on an island of a package by conductive adhesive, and an external connection electrode on the chip are individually connected to predetermined external terminals by use of a wire bonding method, similarly to a typical semiconductor device. The island is connected to any of the external terminals, which is a ground terminal in many cases. In this case, the support substrate can be connected through the island to the ground.
In the SOI semiconductor device, a mounting method or an assembling method such as a chip-on-board method using a flip chip (hereinafter, referred to as COB method) or a tape carrier package (hereinafter, referred to as TCP) method is employed for a higher density mounting method. In this case, as shown in FIGS. 1A and 1B the external connection electrode (not shown) provided on the single crystal semiconductor layer 302 of the chip 110 and a conductive wiring 71 of a wiring substrate 70 to be mounted or an inner lead 80 of TCP are connected to each other through a bump 201. Therefore, there is a problem that it is difficult to apply a potential to the support substrate 301.
If the support substrate is in a floating potential, a potential variation in the support substrate has an adverse influence on an operation of an element, in particular, a threshold potential. As a result, an operation margin of the element is reduced. Also, as disclosed in Japanese Patent No. 2654268, Japanese Laid Open Patent Application (JP-A-Heisei 8-153781) or Japanese Laid Open Patent Application (JP-A-Heisei 8-236754), the breakdown voltage of the element changes depending on the potential of the support substrate. Therefore, if the potential of the support substrate is varied during the operation of the semiconductor element, the breakdown voltage of the element decreases so that there is a possibility of the occurrence of an erroneous operation.
As a method of avoiding the support substrate from being in the floating state, for example, Japanese Laid Open Patent Application (JP-A-Heisei 6-244239) (hereinafter, referred to as a conventional example 1) discloses an example of an SOI semiconductor device in which a potential can be applied from a surface of an element side to the support substrate. FIG. 2 is a sectional view showing the semiconductor device disclosed in the conventional example 1. With reference to FIG. 2, a semiconductor layer 703 of the semiconductor device disclosed in the conventional example 1 is insulated from a semiconductor substrate 701 by an intervening layer insulating film 702. However, conductors 710 are provided on side walls of a concave portion 709 to extend to the semiconductor substrate 701 so that a short-circuit is formed between the semiconductor substrate 701 and a peripheral region 703b. Thus, the same potential as that of the peripheral region 703b is applied to the semiconductor substrate 701. The potential is applied to the peripheral region 703b through a bump 707 from a wiring substrate (not shown), similarly to an element formation region. That is, the potential is applied to the semiconductor substrate 701 from the surface side of the semiconductor layer 703 on which the element is formed.
Also, Japanese Laid Open Patent Application (JP-A-Heisei 2-54554) (hereinafter, referred to as a conventional example 2) discloses a structure in which a semiconductor device is manufactured by use of an SOI substrate and separated into elements by an embedded insulating film. In the conventional example 2, a conductive substrate is used as a lower layer of an insulating film constituting the SOI structure. FIG. 3 is a sectional view showing a main portion of the semiconductor device shown in the conventional example 2. With reference to FIG. 3, the semiconductor device disclosed in the conventional example 2 has a structure in which an insulating film 802 and a conductive semiconductor layer 803 are bonded in this order on a conductive substrate 801. An element body 804 is formed in the semiconductor layer 803. An element separation trench 805 is provided to contact the insulating film 802 at its bottom and to surround the element body 804. The element separation trench 805 is filled with a fill material 814 made of an insulator or polysilicon. The fill material 814 contains therein a conductive fill material 851 made of a p-type polysilicon layer reaching the insulating film 802 from the surface of the element separation trench 805. An opening 821 is formed in the insulating film 802 to connect the conductive fill material 851 and the conductive substrate 801. In the semiconductor device in the conventional example 2, the conductive substrate 801 and an electrode 807 provided on the surface of the fill material 814 are connected by the conductive fill material 851. Thus, the conductive substrate 801 can be used as the conductive material. Therefore, it is possible to reduce the crowded condition of surface wiring lines.
In the semiconductor device of the conventional example 1, the formation of a trench for the element separation region and the formation of a concave trench for a substrate contact are independently carried out as the different processes. Therefore, it is necessary to etch and remove the semiconductor layers 703 at the different positions of the SOI substrate two times. As a result, there is a problem that the manufacturing process becomes long. Also, the structure is designed in such a manner that the route connecting a bump electrode 707 for applying the potential to the support substrate and the support substrate 701 must pass through a peripheral region 703b of the semiconductor layer. Thus, there is another problem that the drop of the resistance in the route is limited.
Also, in the method of manufacturing the semiconductor device in the conventional example 2, a first trench as the trench for the element separation and a second trench having the width wider than that of the first trench are formed at the same time. Also, the insulating film 802 in the bottom of the second trench is etched so that the opening 821 is formed to reach the conductive substrate corresponding to the support substrate 801. In this case, a multi-layer film in which a polysilicon film, a nitride film and an oxide film are laminated is required so as not to etch the other regions. Also, the conductive fill material 851 is formed to connect the electrode 807 and the conductive substrate 801 by implanting impurities such as boron into an insulating polysilicon layer. Thus, there is a limit on the drop in the resistance.
It should be noted that Japanese Laid Open Patent Application (JP-A-Heisei 11-135794) discloses the following semiconductor device. In this reference, the semiconductor device has the CMOS structure in which a pair of offset type MOS transistors of a first conductive type and a second conductive type are provided. The transistors are insulated and separated from each other and are formed on an SOI substrate. In the SOI substrate, first and second substrates of the first conductive type are integrally joined to each other through an embedded oxide film. The transistor of the second conductive type is formed to have an LMOS (Lateral MOS) structure, and the transistor of the first conductive type is formed to have an LDMOS (Lateral Doublexe2x80x94diffused MOS) structure.
Also, Japanese Laid Open Patent Application 2000-31266 (P2000-31266A) discloses the following semiconductor device. In this reference, the semiconductor device has an opening tapered and wider in width than a bottom on a semiconductor substrate. Insulating material is embedded within the opening, and a trench separation film is provided for insulating and separating between elements. The tapered angle between the inner side of the opening and the surface of the semiconductor substrate is equal to or less than 88 degrees. The insulating material is NSG grown by use of a low pressure CVD method.
Therefore, an object of the present invention is to provide a semiconductor device with an SOI structure such as an SOI structure, in which a support substrate and an external connection electrode formed on the surface of a chip are connected to each other through a route of a small resistance, and a method of manufacturing the same.
In an aspect of the present invention, a semiconductor device includes a conductive semiconductor substrate laminated on or bonded to a conductive support substrate through a first insulating film, a separation trench which separates a device formation region where at least a desired element is formed, from a region of the semiconductor substrate, a separation trench, and a substrate contact region where the semiconductor substrate is not present. The semiconductor device further includes a second insulating film which fills the separation trench and covers a surface of the substrate contact region, an external connection electrode formed above the semiconductor substrate, and a support substrate connecting section which passes through the first insulating film and the second insulating film in the substrate contact region to connect the external connection electrode and the support substrate.
Here, the external connection electrode may be formed through a third insulating film on the semiconductor substrate. In this case, the third insulating film may be identical to the second insulating film.
Also, the support substrate connecting section may include a conductive film which is connected with the external connection electrode and covers the second insulating film, and a contact section which passes through the first insulating film and the second insulating film to the support substrate in the substrate contact region. In this case, the conductive film desirably contains a metal film having aluminum as main material.
Also, the contact section may be formed of a single contact. In this case, the single contact may include a refractory metal film formed on side wall of a contact hole for the contact, and the conductive film filling the contact hole in which the refractory metal film is formed.
Also, the single contact may include an additional conductive film which covers side wall of a contact hole for the contact, a refractory metal film formed on the additional conductive film on the side wall of the contact hole, and the conductive film filling the contact hole in which the refractory metal film is formed.
Also, the contact section may include a plurality of contact plugs arranged in an array. In this case, the plurality of contact plugs may be formed of tungsten.
In another aspect of the present invention, a method of manufacturing a semiconductor device is attained by (a) forming at least a desired element in a device forming region of a conductive semiconductor substrate on a chip in which the semiconductor substrate is formed on a conductive support substrate through a first insulating film; by (b) forming trenches which pass through the semiconductor substrate to the first insulating film; by (c) forming a second insulating film on the semiconductor substrate to fill the trenches and to cover a side wall of a substrate contact region; by (d) forming element contact holes for the element to pass through said second insulating film; by (e) forming a contact hole section in the substrate hole region to pass through the first and second insulting films to the support substrate; by (f) filling the element contact hole with first conductive material; by (g) filling the contact hole section with second conductive material; by (h) forming a conductive film connected to the contact hole section; and by (i) forming an external connection electrode connected to the conductive film.
Here, the (d) forming step and the (e) forming step may be carried out at a same time.
Also, when the (d) forming step includes a first exposure step and the (e) forming step includes a second exposure step, the first exposure step and the second exposure step may be individually carried out. In this case, the (d) forming step and the (e) forming step may be carried out at a time, except for the first exposure step and the second exposure step.
Also, the (f) filling step and the (g) filling step may be carried out at a time.
Also, the (e) forming step may include the step of forming a single contact hole in the substrate hole region. In this case, the (g) filling step and the (h) forming step may be carried out at a same time.
Also, the (e) forming step may include the step of forming a plurality of contact holes arranged in an array in the substrate hole region.